Comparisons are a bit hard because (perhaps outside of some specialty--and more expensive--gaming systems) what you build yourself is arguably "better"/more optimized than a random HP or Dell box. At the same time, the percentage of people who care about optimization at that level is pretty small. I built/upgraded PCs for years and now I pretty much have zero interest.

But again to the basic point, it's certainly close to a wash which wouldn't be true with most things.